The present invention concerns a method of pumping a pumpable product by means of a pump unit containing two pump chambers and a common control, which regulates the flow between the pump chambers and the unit's in- and out-flow.
With regular dispensing of a pumpable product by means of, e.g., a piston pump, an intermittent flow unavoidably arises in the pipe leading to the pump. This entails that pressure shocks arise in the pipe. With fast, regular dispensing of a product these pressure shocks can become very powerful and entail such serious damage to the pipe and its suspension that leakage arises.
Dosing pumps in the form of piston pumps are often used in industries such as the packaging industry. More particularly, piston pumps are often used in those filling machines which are used for filling bottles or packaging containers with liquid-state contents, e.g., various dairy products such as milk, sour milk and yogurt, or soups. Since packaging machines of this kind often work at high speed, pressure shocks in the pipe are a serious problem. The usual way of solving this is to provide the pipe with some form of pressure compensation device. In practice a tank is used or a level vessel in the form of a closed tank which is series-connected to the pipe and sometimes balanced with the aid of pressurized gas. The level in the tank is allowed to vary within certain limits and in this way pressure shocks between the pump and the tank can be compensated so that they do not spread any further to the pipe.
Even if the use of a compensation tank avoids the problem with pressure knocks, other problems are created instead, especially when the technique with a compensation tank is employed within the food industry, since the tank constitutes an irregularity in the pipe which thereby becomes difficult to wash in a satisfactory manner. With the type of packaging system that aseptically packages sterile foods, it is, in practice, impossible to wash and sterilize the tank in a rational manner, at least when several highly viscous products or products containing particles, e.g. soups, are to be packaged. A system with a compensation tank, which may also be provided with devices for being pressurized with inert gas, is, in addition, very expensive, particularly if it has to be made in a washable and sterilizable manner. With fast packaging machines, where a number of dosing pumps are used, the costs are increased.